Polypyrrolidone fiber for activating sensor means in a humidity responsive device

ABSTRACT

A device responsive to changes in humidity is provided in which at least one strand of polypyrrolidone fiber is disposed between a stanchion and spring means, changes in the humidity being detected by means responsive to contraction and expansion of the polypyrrolidone strand.

Cite States Patent 1191 Tozer 1 1 Oct. 2, 1973 POILYIPYRROILIDONE FIBERIFOIR ACTIVATHNG SENSOR MEANS IN A HUMIDITY RESPONSHVIE DEVICE [75}Inventor: Job R. Tozer, Dallas, Tex.

[73] Assignee: Alrac Corporation, Stamford, Conn.

[22] Filed: Jan. 6, 11972 211 Appl. No.: 215,740

1521 11s. c1 ..2110/61.06,73/337.5,236/44 A, 260/78 P 1511 11111.0.11110111 35/42 1581 Field 01 Search ZOO/61.06; 236/44 A, 236/44 0;260/78 P; 73/337, 337.5

[56 References Cited UNITED STATES PATENTS 3,288,961 1 1/1966 ThompsonZOO/61.06

3,686,066 8/1972 Peters 260/78 1 X 2,509,593 5/1950 Goddard 1 2,210,6568/1940 Downs et a1.

3,563,458 2/1971 Martin 3,683,046 8/1972 Jarovitzky .1

3,681,296 8/1972 Burks, Jr.

3,682,869 8/1972 Jarovitzky 260/78 P 3,143,610 8/1964 GustafsonZOO/61.06

Primary Examiner-l R. Scott Attorney.|acobs & Jacobs [57] ABSTRACT Adevice responsive to changes in humidity is provided in which at leastone strand of polypyrrolidone fiber is disposed between a stanchion andspring means, changes in the humidity being detected by means responsiveto contraction and expansion of the polypyrrolidone strand.

10 Claims, 6 Drawing Figures PAIENTED OCT 2 I975 SHEET 2 OF 4 FIG. 4A

fl f/U i X x u? c I// o o o I 0 y o o 0 h n x u 0 00 x r O K 0 x: 1 O XL0 X Cd Ru Ru Ru 5 m 6 m 5 w 4 3 2 PATENTEDflcI 2191s INDICATED RELATIVEHUMIDITY SIIEEI F 4 POLYPYRROLIDONE xxxxxx. ANIMAL MEMBRANE NYLON 6HUMAN HAIR .3"/o ERROR LINE 7O 8O 9O I00 ACTUAL RELATIVE HUMIDITYPATENTEDUBT 2 a. 76-3 .338 SHEET a nr 4 POLYPYRROLIDONE FIBER FORACTIVATING SENSOR MEANS IN A HUMIDITY RESPONSIVE DEVICE DETAILEDDESCRIPTION The present invention pertains to an improved humidityresponsive device which can be employed either for a direct reading ofrelative humidity or in association with humidity control equipment.

It is an object of the present invention to provide a humidityresponsive device which accurately reflects the relative humidity over awide range of normal atmospheric conditions.

A further object of the present invention, consistent with the foregoingobject, is to provide a humidity responsive device which issubstantially insensitive to temperature changes encountered in normalatmospheric conditions.

A still further object of the present invention is to provide a humidityresponsive device which, once adjusted, requires little or no furtheradjusting so as to be suitable for, among other applications, remoteinstallation.

These and other objects of the present invention will become apparentfrom the following description and the attached drawings in which:

FIG. I is a schematic representation of one embodiment of the presentinvention in which the humidity responsive device provides readings ofrelative humidity through association with an appropriate dial andpointer;

FIG. 2 is an elevation of a second embodiment of the present inventionin which the humidity responsive device is associated with switchingmeans which, in turn, may be employed in the activation of humiditycontrol equipment (not shown);

FIG. 3 is a top view of the embodiment depicted in FIG. 2;

FIG. 4A and 4B are a plotting of actual relative humidity to recordedrelative humidity with the sensing element of the present device andwithvarious other humidity responsive materials; and

FIG. 5 is a schematic representation of a further embodiment utilizingelectrical reading means.

Referring now to FIG. 1 in greater particularity, there is provided abase 10 on which is mounted stanchion ll. Pivotably mounted to the baseis a swing lever 12. Fixed between swing lever 12 and stanchion 11 is atleast one strand of polypyrrolidone fiber 13. Spring means 14areprovided to urge swing lever I2 in tensional opposition to thepolypyrrolidone strand. Stanchion II is associated to base 10 throughnull adjust 15 so that the tensional stress of the polypyrrolidone fiberstrand can be adjusted. Attached to the-"opposing end of swing lever 12are means operable to detect movement of the lever. This comprises apulley l6 pivotably mounted on base 10, a wire or string 17 attached toswing lever 12 and coiled about pulley l6. Rotational motion of pulleyI6 is transmitted through any appropriate train to pointer 18.

In FIGS. 2 and 3, swing lever 12a activates switch 19 mounted on base10a, the tensional opposition of swing lever 12a to the polypyrrolidonestrand 13a being provided by switch button 19a. In addition to beingattached to swing lever 12a, polypyrrolidone strand 13a is also attachedto stanchion 11a. Adjustments on the tension of polypyrrolidone strand13a are effected through use of the null adjust 15a in opposition tospring 20.

In FIG. 5, the strand of polypyrrolidone 13b is attachedat one end tostanchion lllb through null adjust 15b and at the other end to magneticrod 21. Magnetic rod 21 is in turn attached to spring means 14!: whichmaintains tension on strand 13b. Surrounding magnetic rod 21. andmounted on base 10b is electromagnetic pickup 22 which is electricallyconnected to responsive means 23 (either readout, transmittal orcontrol) through connectors 24. In place of inductive sensing means, onecan employ a capacitive sensor in the apparatus of FIG. 5 oralternatively a pneumatic or hydraulic sensor.

As noted in connection with FIGS. ll, 2, 3 and 5, the humidityresponsive device of the present invention employs as its key componentat least one strand of polypyrrolidone fiber fixed between spring means15, 15a and 15b and stanchion 11 or 11a, respectively, either directlyas in FIG. 5 or through swing lever 12 or 12a in FIGS. 1, 2 and 3. Theunique humidity responsive properties of polypyrrolidone fiber permits adirect and linear reading of relative humidity over a wide range and anearly linear reading over even a wider range. This can be seen in FIGS.4A and 4B. Thus from 40 percent relative humidity to percent relativehumidity, the response of polypyrrolidone is linear when measured at80F. An accuracy well within 1 2.5 percent is observed when thetemperature is ranged from 40F to F. In this range, the sensitivity ofpolypyrrolidone is approximately 0.0013 in./in./% RH. The materialexhibits virtually no hysteresis. Although there is some loss oflinearity of response below 40 percent relative humidity, it isrelatively small, largely within the 3 percent error factor, and easilycompensated, as for example through utilization of non-linear readoutindicia at the lower end of the indicator dial. As a result of itsexceptional linearity of response to humidity changes, polypyrrolidonerepresents a significant improvement over substances heretofore employedas humidity sensors such as human hair, nylon-6, and animal membranes,such as goat gut, none of which provide such a linear response. Inaddition, polypyrrolidone is exceptional in its absence of hysteresis,minimal temperature deviations, and freedom from fatigue.

Although numerous references describing polymers of pyrrolidone exist,the specialized requirements for the material employed in the presentinvention are satisifed only with the recently available polymers of 2-pyrrolidone which are capable of forming white fiber by melt extrusionand having an inherent viscosity of at least about 2.5 dl/g, expressedin terms of a 0.5 g/dl solution in hexafluoroisopropanol at 30C. Suchmaterial can be ,prepared when Z-pyrrolidone is polymerized in thepresencepf an alkaline polymerization catalyst and .carbon dioxide,generally at least 0.01 percent by weight of carbon dioxide, based onthe weight of 2- pyrrolidone monomer. These polymers of 2- pyrrolidoneand the method of their preparation are described in detail in SouthAfrican Patent No. 69/1727. It has been found that only polypyrrolidonesuch as that which is produced in accordance with this method can it bereadily melt extruded into the long fibers necessary to produce thespecial characteristics required for the present invention. Hence thepolymer of Z-pyrrolidone which is suitable for use in the present devicewill have the ability after a 5 gram sample is held at 270C. under apressure of 6.7 X dy'nes/cm in a Slocum melt indexer having a singlehole spinnerette of 20 mils in diameter and 80 mils in length for 4minutes to form a continuous filament for at least 3 minutes after thespinnerette hole is opened.

Returning now to FIGS. 1 3 and 5, it will be observed that the strand ofpolypyrrolidone is fixed between stanchion ll, 11a or 11b and springmeans 14, 20 or 14b, respectively. While in its simplest embodiment, asingle strand of polypyrrolidone is employed, the sensitivity of theentire device can be increased through utilization of a plurality ofstrands. These may be a series of strands, each attached to thestanchion and swing lever, or may be a single strand passed over each ina continuous loop. The length of the polypyrrolidone strand 13 and 13ais a matter of choice; generally it has been found that a length of fromone to two inches, preferably about one and a half inches, providessatisfactory results.

In operation, the device is installed and corrected to the actualrelative humidity, as determined for example through the use ofa drybulb hygrometer, through utilization of null adjust 15 or 15a.Subsequent increases in humidity will effect a lengthening of thepolypyrrolidone strand l3 and 130. In the embodiment shown in FIG. 1,this lengthening will release the tension on wire 17, thereby causingspring means 14 to urge pulley 16 in a counterelock-wise direction, thisrotation being, in turn, transferred to pointer 18 for the appropriatereaddown on a dial (not shown). A corresponding reduction in humiditywill cause a contraction of polypyrrolidone strand 13 and thiscontraction will, in; turn, be transmitted to a dial through pointer 18in a similar fashion to that described above. In the embodiment shown inFIGS. 2 and 3, an increase in humidity will cause a lengthening ofpolypyrrolidone strand 13a and swing lever 120 will thus be urged awayfrom the switch button 19a of switch 19. Upon a decrease in relativehumidity, polypyrrolidone strand 13a will contract, causing swing lever12a to depress switch button 19a and thereby activate the particularcircuit involved. In the apparatus of FIG. 5, humidity responsivecontractions or expansions of polypyrrolidone strand 13b causescorresponding movements of magnetic rod 21. These movements produce anelectrical signal in coil 22 through inductance which signal istransmitted to response means 23. Response means 23 may be a simplereadout mechanism, a recording mechanism, a control mechanism ortransmitting mechanism as in a remote installation. As noted the sensormay be of the capacitive,hydraulic or pneumatic rather than inductivetype.

The foregoing description and drawings represent typical embodiments ofthe present invention but are not intended as a limitation on the scopethereof, it being apparent that the invention can be practiced throughobvious modifications and rearrangements without departing from theessential spirit thereof.

What is claimed is:

1. A humidity responsive device comprising a base, a stanchion mountedon said base, at least one strand of polypyrrolidone fiber attached tosaid stanchion, spring means operative to maintain said polypyrrolidonestrand in tensional opposition to said stanchion, means for adjustingthe tensional stress of said strand, and sensor means operable to detecthumidityresponsive expansion or contraction of said strand ofpolypyrrolidone.

2. A humidity responsive device according to claim 1 wherein saidpolypyrrolidone is a melt extruded fiber of a polymer of 2-pyrrolidonehaving an inherent viscosity of at least about 2.5 dl/g obtained throughthe polymerizaton of Z-pyrrolidone in the presence of an alkalinepolymerization catalyst and the presence of carbon dioxide.

3 A humidity responsive device according to claim 2 wherein a pluralityof strands of polypyrrolidone fiber are disposed between said springmeans and said stanchion.

4. A humidity responsive device according to claim 3 wherein the saidsensor means operable to detect expansion and contraction of saidpolypyrrolidone strands is a dial and pointer.

5. A humidity responsive device according to claim 3 wherein said sensormeans operable to detect expansion and contraction of saidpolypyrrolidone strands is an electrical switch.

6. A-, humidity responsive device according to claim 3 wherein saidsensor means operable to detect expansion and contraction of saidpolypyrrolidone strands is an inductive transducer.

7. A humidity responsive device according to claim 3 wherein said sensormeans operable to detect expansion and contraction of saidpolypyrrolidone strands is a capacitive transducer.

8. A'humidity responsive device according to claim 3 wherein said sensormeans operable to detect expansion and contraction of saidpolypyrrolidone strands is a pneumatic sensor.

i 9. A humidity responsive device according to claim 3 wherein saidsensor means operable to detect expansion and contraction of saidpolypyrrolidone strands is a hydraulic sensor.

10. A humidity responsive device according to claim 1 furthercharacterized in that a swing lever is pivotably mounted on said base,and a plurality of strands of polypyrrolidone fiber are disposed betweensaid swing lever and said stanchion, said spring means being operativeto urge said swing lever in tensional opposition to said stanchionthrough said strands.

2. A humidity responsive device according to claim 1 wherein saidpolypyrrolidone is a melt extruded fiber of a polymer of 2-pyrrolidonehaving an inherent viscosity of at least about 2.5 d1/g obtained throughthe polymerizaton of 2-pyrrolidone in the presence of an alkalinepolymerization catalyst and the presence of carbon dioxide. 3 A humidityresponsive device according to claim 2 wherein a plurality of strands ofpolypyrrolidone fiber are disposed between sAid spring means and saidstanchion.
 4. A humidity responsive device according to claim 3 whereinthe said sensor means operable to detect expansion and contraction ofsaid polypyrrolidone strands is a dial and pointer.
 5. A humidityresponsive device according to claim 3 wherein said sensor meansoperable to detect expansion and contraction of said polypyrrolidonestrands is an electrical switch.
 6. A humidity responsive deviceaccording to claim 3 wherein said sensor means operable to detectexpansion and contraction of said polypyrrolidone strands is aninductive transducer.
 7. A humidity responsive device according to claim3 wherein said sensor means operable to detect expansion and contractionof said polypyrrolidone strands is a capacitive transducer.
 8. Ahumidity responsive device according to claim 3 wherein said sensormeans operable to detect expansion and contraction of saidpolypyrrolidone strands is a pneumatic sensor.
 9. A humidity responsivedevice according to claim 3 wherein said sensor means operable to detectexpansion and contraction of said polypyrrolidone strands is a hydraulicsensor.
 10. A humidity responsive device according to claim 1 furthercharacterized in that a swing lever is pivotably mounted on said base,and a plurality of strands of polypyrrolidone fiber are disposed betweensaid swing lever and said stanchion, said spring means being operativeto urge said swing lever in tensional opposition to said stanchionthrough said strands.